Expression 12: "a" left parenthesis, "x" minus "x" Subscript, 1 , Baseline , right parenthesis plus "b" left parenthesis, "y" minus "y" Subscript, 1 , Baseline , right parenthesis equals 0ax−x1+by−y1=0
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Expression 13: "a" equals negative left parenthesis, "P" Subscript, 1 , Baseline minus "f" Subscript, 1 , Baseline , right parenthesisa=−P1−f1
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Expression 14: "b" equals negative left parenthesis, "P" Subscript, 2 , Baseline minus "f" Subscript, 2 , Baseline , right parenthesisb=−P2−f2
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Expression 15: left parenthesis, "x" Subscript, 2 , Baseline plus left parenthesis, "l" "R" minus "x" Subscript, 2 , Baseline , right parenthesis "t" , "y" Subscript, 2 , Baseline minus "y" Subscript, 2 , Baseline "t" , right parenthesisx2+lR−x2t,y2−y2t
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Expression 16: left parenthesis, left parenthesis, "l" "R" , right parenthesis "t" , 0 "t" , right parenthesislRt,0t
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Expression 17: negative "b" left parenthesis, left parenthesis, "l" "R" , right parenthesis "t" Subscript, 2 , Baseline minus "x" Subscript, 2 , Baseline , right parenthesis plus "a" left parenthesis, 0 "t" Subscript, 2 , Baseline minus "y" Subscript, 2 , Baseline , right parenthesis equals 0−blRt2−x2+a0t2−y2=0
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Expression 18: "t" Subscript, 2 , Baseline equals StartFraction, negative "b" "x" Subscript, 2 , Baseline plus "a" "y" Subscript, 2 , Baseline Over negative "b" left parenthesis, "l" "R" , right parenthesis , EndFractiont2=−bx2+ay2−blR
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Expression 19: "x" Subscript, 3 , Baseline equals left parenthesis, "l" "R" , right parenthesis "t" Subscript, 2 , Baselinex3=lRt2
Expression 21: left parenthesis, "x" Subscript, 2 , Baseline plus left parenthesis, "x" Subscript, 3 , Baseline minus "x" Subscript, 2 , Baseline , right parenthesis "t" , "y" Subscript, 2 , Baseline plus left parenthesis, "y" Subscript, 3 , Baseline minus "y" Subscript, 2 , Baseline , right parenthesis "t" , right parenthesisx2+x3−x2t,y2+y3−y2t